Bump actions/checkout from 4 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 4 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v4...v6)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -37,7 +37,7 @@ jobs:
           go-version: ${{ env.GO_VERSION }}
           cache: false # see actions/setup-go#368
 
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - uses: golangci/golangci-lint-action@v6
         with:
           version: v1.61.0
@@ -59,7 +59,7 @@ jobs:
           go-version: ${{ env.GO_VERSION }}
           cache: false # see actions/setup-go#368
 
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           path: src/github.com/containerd/plugin
           fetch-depth: 25
@@ -75,7 +75,7 @@ jobs:
     timeout-minutes: 5
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           path: src/github.com/containerd/plugin